Unit 24 Quiz Flashcards

1
Q

When replacing a TXV, what are three key identifying features you should look for?

A

The amount of revolutions/turns the original is adjusted to

The diameter dimensions of the original TXV

orientation/positioning of original TXV

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2
Q

The diaphragm in the TXV responds to three different pressures which act at the proper time to open, close or modulate the valve needle between open and closed. What are those three pressures?

A

Evaporator pressure, sensing bulb pressure, spring pressure

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3
Q

Charged with a fluid different from the system fluid.

A

Cross liquid

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4
Q

Instructions or programs stored in the microprocessor.

A

Algorithms

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5
Q

Contains a small amount of liquid refrigerant. Sometimes called a “critical charge” bulb. Also referred to as a maximum operating pressure valve.

A

Vapor charge bulb

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6
Q

Controls refrigerant flow by pressure drop. Calibrated by length and inside diameter.

A

Capillary tube

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7
Q

Metering valve that uses a thermistor as a temperature sensing element that varies the voltage to a heat motor operated valve.

A

Electronic expansion valve

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8
Q

Used to maintain constant pressure in the evaporator. Will starve refrigerant when suction pressure rises.

A

Automatic expansion valve

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9
Q

Difference between the superheat set point of the controller and the actual superheat.

A

Error/offset

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10
Q

Small storage tank located between the condenser and expansion device. Stores excess refrigerant during different load conditions and when servicing the system.

A

Refrigerant receiver

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11
Q

Communication between sensor and controller to open or close the valve.

A

Feedback loops

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12
Q

Used when an evaporator has a very long circuit or multiple circuits and a pressure drop occurs between the expansion valve outlet and the evaporator inlet.

A

External equalizer

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13
Q

What are the four types of sensing bulb charges?

A

Liquid, vapor, cross liquid, cross vapor

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14
Q

Superheat spring pressure is 10.4 psig, sensing bulb pressure is 51.2 psig and the evaporator pressure is 35.1 psig. Will the TXV open, close or remain in equilibrium?

A

Open

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15
Q

What type of sensing bulb charge is also known as a “critical charge” bulb?

A

The vapor (Gas) charge bulb

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16
Q

The best position for mounting a TXV sensing bulb on tubing less the 3/4” diameter is ______.

A

12 o’clock position

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17
Q

True or false: If the TXV valve body, that uses a vapor charged sensing bulb, becomes colder than the sensing bulb, the sensing bulb may not operate because the vapor in the sensing bulb has condensed and migrated to the colder valve body.

A

True

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18
Q

True or false: A balanced port TXV can be readily identified by its external equalizer tube.

A

False

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19
Q

True or false: An automatic expansion valve’s (AXV) sensing bulb must be mounted at the 5 o’clock position on the suction line at the exit of the evaporator.

A

False

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20
Q

True or false: Do not use plastic zip ties to secure the sensing bulb in place.

A

True

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21
Q

True or false: As the load increases on the evaporator, the TXV will adjust and pressure in the evaporator will increase.

A

True

22
Q

True or false: The automatic expansion valve maintains a constant superheat in the evaporator.

A

False

23
Q

True or false: The pressure limiting TXV is desirable in a low temperature applications because it keeps the suction pressure to the compressor down during hot pull downs.

A

True

24
Q

When the evaporator pressure drops, the automatic expansion valve will open to allow more refrigerant to enter the evaporator.

A

True

25
Q

The term “offset” and “error” are interchangeable.

A

True

26
Q

A vapor charge sensing bulb does not have any liquid in it.

A

False

27
Q

True or false: Proportional modes can only be used in closed loop feedback applications like that of the EEV.

A

True

28
Q

What can be done to improve the sensitivity/accuracy of a sensing bulb?

A

*Clean the tubing before placing sensing bulb
*Use proper fasteners for the sensing bulb to ensure sensing bulb is securely positioned.

29
Q

Why is the TXV sensing bulb not placed at the 6 o’clock position on the suction line?

A

Because of the oil potentially acting as an insulator

30
Q

How is a TXV mounted if the description says the fittings are ODF?

A

The TXV would be mounted utilizing solder

31
Q

The purpose of the capillary tube is to _________.

A

Regulate the flow of refrigerant into the evaporator, lower the pressure of the liquid refrigerant, lower the boiling point of the refrigerant.

32
Q

If a sensing bulb must be mounted vertically, how is the position of the transmission tube oriented?

A

Transmission tube should be pointed up

33
Q

What are the recommended superheat settings for low temperature evaporators?

A

2 - 5 degrees

34
Q

How is the TXV mounted if the description says FPT?

A

Female flange mounted

35
Q

When a TXV uses on ODF type mount, what safety precaution(s) must you take when mounting it?

A

Protect valve/TXV with paddy or paste

36
Q

If the sensing bulb assembly of a TXV develops a leak, what will occur?

A

Doesn’t allow TXV to open to let refrigerant in

37
Q

Where is the TXV sensing bulb mounted?

A

Outlet of the evaporator coil on the suction line before the “T” if there is an internal equalizer

38
Q

Balanced port TXVs are used to _____ ambient temperatures.

A

Feed refrigerant at a normal rate with low

39
Q

What happens when a sensing bulb is placed after the equalizer junction on the suction line? (Explain in detail and how can you detect if something is wrong with the equalizer)

A

The temperature measurement will be inaccurate, resulting in improper system operation. Visually inspecting the equalizer components can assist in finding or ruling out potential leaks & blockage. Inaccurate temperatures can mean equalizer problem

40
Q

What pressures are acting upon the diaphragm in an automatic expansion valve?

A

Evaporator pressure & spring & atmospheric pressure

41
Q

How does integral controller affect proportional controller?

A

By enhancement, by adding an integral controller to a proportional controller, the modified output signal will assist in the enforcement of off setting valve to zero.

42
Q

True or false: The term differential and derivative are used interchangeably.

A

True

43
Q

Answer the following questions using the disassembled TXV. Type refrigerant, FJ, R-12, R-134A, R-401A, R-513A:

What is the capacity for this TXV?

A

A quarter ton 1/4 nominal capacity

44
Q

Answer the following questions using the disassembled TXV. Type refrigerant, FJ, R-12, R-134A, R-401A, R-513A:

What is the element size for this TXV?

A

43

45
Q

Answer the following questions using the disassembled TXV. Type refrigerant, FJ, R-12, R-134A, R-401A, R-513A:

How many different refrigerants can this TXV be used with?

A

4

46
Q

Answer the following questions using the disassembled TXV. Type refrigerant, FJ, R-12, R-134A, R-401A, R-513A:

Does this TXV use an equalizer?

A

Yes

47
Q

Answer the following questions using the disassembled TXV. Type refrigerant, FJ, R-12, R-134A, R-401A, R-513A:

How is this TXV mounted in a system?

A

SAE flare mount

48
Q

Answer the following questions using the disassembled TXV. Type refrigerant, FJ, R-12, R-134A, R-401A, R-513A:

How many superheat spring guide(s) does this TXV use and where is/are they located?

A

2
One on top of the spring and another at the bottom of the spring

49
Q

What material is the valve pin made of?

A

Stainless steel

50
Q

What is the three letter designation for the type of mount used in #47 above?

A

SAE flare (internal equalizer)
Valve type
Refrigerant compatibility